Hi.  I would like to second the headless/non-GUI mode for /*nix/i systems.  It would be useful to be able to start the Bitcoin software from an initscript or one's ~/.bashrc (or equivalent) file and let it run in the background, silently cranking away.

Also, what would the feasibility of changing the location of the wallet.dat file be for the Win32 client?  I ask this because I was playing around with the .zipped Windows Bitcoin client yesterday, and it struck me that it would make a good portable application.  I was toying with the idea of decompressing it into a TrueCrypt volume on a USB drive so that it could, say, be taken on the road, run for a few hours, and then shut down just before the volume was unmounted, but it created the wallet.dat file in the C:\Documents and Settings\username\Application Data\Bitcoin directory.  In effect, using a portable version of Bitcoin to eventually grow a portable wallet.